1. Technical Field of the Invention
The present invention relates generally to a pulse motor driver, and more particularly to an improvement on a pulse motor driver, for use in an odometer for automotive vehicles, designed for reducing mechanical noise which is produced in a gear train of the odometer and which would make vehicle occupants feel uncomfortable during traveling at relatively low speeds.
2. Background Art
Usually, pulse motors are used, as simple positioning motors which may be controlled by an open loop system, for mechanically operating some vehicular equipment. For example, Japanese Utility Model First Publication No. 2-80872 teaches a pulse motor employed in a vehicle odometer. This prior art pulse motor, however, has a drawback in that it rotates quickly in stepwise fashion upon input of exciting pulse signals, causing mechanical noise to be produced due to the backlash of a gear train or so forth. To overcome this problem, it has been proposed in the art that interphase capacitors are so arranged between phase coils of a pulse motor as to provide a delay serving to have an exciting current rise gradually for preventing the pulse motor from rotating suddenly.
Such an approach, however, encounters another drawback in that since a resistance of phase coils is usually small, it is necessary to increase the capacity of a capacitor for providing a sufficient delay. This will lead to a bulky circuit structure.